:(
She is a terrier cross and it's under her armpit/ side of her chest.
It's squishy and mobile and apparently causes her no pain. All of which according to Vet google, is good news.
My exe's elderly border collie had a number of these and they were harmless fatty lumps.
I am still worried though and will have it checked out.
She's my heartdog and can't bear the thought of anything happening to her. She's 12 this year and I love every greying hair on her little body.